Also indefensible with the "only what is most popularly searched on" [argument]...
Google doesn't claim that autocomplete shows the most-popular searches. I don't know if there's an official description of the the process, but while the base algorithm is no doubt a fairly simple predictor (probably something like an HMM doing Viterbi, though they might just be reusing one of their ANN implementations), it's likely that personal search history is also an input, if Google can identify you by session, cookie, or other means.
More importantly, Google lets people request particular autocomplete results be removed. So it's quite possible that one organization (say, a particular political party) has a small team of interns looking for autocomplete results and submitting removal requests to Google, while another organization is less vigilant.
A conspiracy seems rather less likely, since it's quite cheap for organizations to arrange this state of affairs themselves.